Nitric oxide synthase activity in the abdominal aorta of rats is decreased after 4 weeks of simulated microgravity.

1. The aim of the present study was to investigate the effects of simulated microgravity on the arterial dilatory responsiveness and L-arginine (L-Arg)-nitric oxide (NO)-cGMP pathway in the abdominal aorta of rats. 2. Twenty healthy male Sprague-Dawley were randomly divided into control and simulated microgravity groups. Rats in the simulated microgravity group were subjected to hindlimb unweighting (HU). After 4 weeks, arterial dilatory responsiveness was examined in vitro in isolated abdominal aortic rings. Western blotting was used to measure endothelial (e) and inducible (i) NO synthase (NOS) protein content. Total concentrations of nitrate and nitrite (NO(x)), the stable metabolites of NO, were determined by the chemiluminescence method. Nitric oxide synthase activity in the abdominal aorta was determined through the conversion of [(3)H]-L-Arg to [(3)H]-L-citrulline. 3. The data showed that the dilatory responses of the arterial rings to L-Arg and acetylcholine decreased in rats exposed to simulated microgravity, but the dilatory responses to sodium nitroprusside and 8-bromo-cGMP were similar in both simulated microgravity and control rats. The expression of eNOS and iNOS did not differ significantly between the two groups. The NO(x) concentration in the abdominal aorta of HU rats was significantly less than that in control rats. Nitric oxide synthase activity in the aorta decreased after 4 weeks of HU. 4. The data indicate that endothelium-dependent vasorelaxation in the abdominal aorta decreased due to 4 weeks of simulated microgravity in rats and that this impaired dilatory responsiveness may result from decreased NOS activity.

[The pharmacological correction of hemodynamics during the simulation of the early period of adaptation to weightlessness]. / Farmakologicheskaia korrektsiia gemodinamiki pri modelirovanii rannego perioda adaptatsii k nevesomosti.

Investigations of volunteered subjects in whom antiorthostatic hypokinesia was modeled by tilting the cranial end of the body by -15 degrees were to answer whether pharmacological countermeasures of the vestibular/autonomous syndrome (motion sickness, sea sickness) alter the orthostatic tolerance and cardiovascular parameters. As was stated, the drugs allow controlled correction of hemodynamic resistance to the head-down tilt. Ephedrine, phencarol, ephedrine combined with scopolamine and pipolphen, and stugeron normalized cerebral circulation. Medicaments were unable to moderate the sympathoadrenal reaction to the head-down tilt; however, blood concentrations of catecholamines were significantly lower than in the control. The greatest effect was achieved using ephedrine and ephedrine plus pipolphen.

[The effect of support loads and CNS stimulants on the development of the atrophic process in the muscles of suspended rats]. / Vliianie opornykh nagruzok i stimuliatorov TsNS na razvitie atroficheskogo protsessa v myshtsakh vyveshennykh krys.

The histomorphometric method there was used to study effects of ephedrine, strychnine, and support loads on the atrophy of m. soleus and m. gastrocnemius in rats with load-deprived lower extremities (14-day tail-suspension). Deficiency of support loads on the lower extremities led to atrophy of the muscles, especially the slow m. soleus. Injections of ephedrine (0.06 mg/kg), strychnine (0.015 mg/kg) as well as ephedrine and strychnine at one and the same time did not affect the development of atrophy. On the contrary, daily 2-hr support loading of the rear extremities had a favourable effect on the muscle atrophy as it was slowed down. Particularly effective were injections of ephedrine on the background of support loads following which the mass of m. soleus in the suspended rats was close to vivarium control. It is suggested that the preventive effect of ephedrine is associated with stimulating the CNS controllers of the somatotropic function of the pituitary body and eventual enhancement of the somatotropic hormone production.

[The development of the syndrome of congestive parenchymatous organs under conditions of short-term hypokinesia]. / Razvitie sindroma zastoinykh parenkhimatoznykh organov v usloviiakh kratkovremennoi gipokinezii.

Five series of head-down (-10 degrees to -30 degrees, up to 18 hr) tilt tests were performed with participation of 65 healthy male subjects. The ultrasonic technique was used to investigate the liver, spleen, pancreas, kidney, and the main abdominal vessels, i.e. aorta in the abdomen and superior mesenteric artery, interior caval, portal, and splenic veins. A few hours of HDT already brought about a complex of load-deprivation reflexes (the syndrome of stagnant parenchymal organs) characterized by a prolonged venous congestion in the abdominal organs-vessels system, increases in sizes and blood filling of the liver, spleen, pancreas, kidney, and the main arteries and veins in this hemodynamic region. This was the first time when increases in pancreas including its head, body and tail, and the abdominal blood vessels were quantified at the beginning of adaptation to HDT. The load-deprivation reflexes arising in this period were hemodynamic by nature. Considering the significant functional strain of the abdominal organs and vessels and particularly the limited control of excessive blood flow towards the pancreas and kidneys, there is a good reason to look into the ways to improve the existing countermeasures against the consequences of immobilization for humans both in general clinic and preventive medicine, and in short- and long-term space missions.